Method and apparatus for separating composite member using fluid

ABSTRACT

To separate a composite member consisting of a plurality of bonded members without destructing or damaging it, a fluid is jetted against the composite member from a nozzle to separate it into a plurality of members at a position different from a bonding position.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forseparating a composite member, separated members, and a semiconductorsubstrate and its production method.

[0003] 2. Related Background Art

[0004] The formation of a single crystal Si semiconductor layer on aninsulating surface of a substrate is widely known as a semiconductor oninsulator (SOI) technique, and many efforts have been made to researchthis technique because devices produced using the SOI technique havemany advantages that cannot be achieved by bulk Si substrates used tofabricate normal Si integrated circuits.

[0005] The use of the SOI technique provides the following advantages:

[0006] (1) The dielectric separation can be easily made to attain highintegration.

[0007] (2) Radiation resistance is excellent.

[0008] (3) The stray capacity is reduced to attain high speed.

[0009] (4) The well formation process can be omitted.

[0010] (5) Latch-up can be prevented.

[0011] (6) The thickness can be reduced to provide a fully depletedfield effect transistor.

[0012] To achieve the many advantages of the device, methods for formingSOI structures have been researched for decades. One of such knownmethods is SOS (silicon on sapphire) in which Si is heteroepitaxiallyformed by CVD (chemical vapor deposition) on a single crystal sapphiresubstrate. This technique has been successful as the maturest SOItechnique, but its applications are limited by a large amount of crystaldefects due to the misalignment of lattices in the interface between anSi layer and a sapphire substrate, by the mixture of aluminum from thesapphire substrate into the Si layer, and in particular, by the highcosts of the substrate and the still insufficient the enlargement ofarea of the device. More recently, an attempt has been made to implementan SOI structure without the sapphire substrate. This attempt can beroughly classified into the following two methods.

[0013] 1. After the surface of an Si single crystal substrate isoxidized, a window is made in the oxidized film to expose a part of thesurface of the Si substrate, and this part is used as a seed to allow ahorizontal epitaxial growth to form an Si single crystal layer on theSiO₂ (in this case, an Si layer is deposited on SiO₂).

[0014] 2. The Si single crystal substrate is used as an active layer andSiO₂ is formed under this layer (this method does not require an Silayer to be deposited).

[0015] Known means for realizing the above method 1 include a method forallowing the direct horizontal epitaxial growth of single crystal layerSi using CVD, a method of depositing amorphous Si and allowing itshorizontal epitaxial growth in a solid phase by thermal treatment, amethod of irradiating an amorphous or polycrystal Si layer withconverging energy beams such as electron or laser beams, and allowing asingle crystal layer to grow on SiO₂ by means of meltingrecrystallization, and a method of using a bar-like heater to scan amolten area in such a way that the scanning trace appears like a band(zone melting recrystallization). Although these methods have bothadvantages and disadvantages, they still have many problems in terms oftheir controllability, productivity, uniformity, and quality and none ofthem have been put to industrially practical use. For example, the CVDmethod requires sacrificial oxidization to provide flat films. The solidphase growth method provides poor crystallinity. The beam anneal methodhas problems in terms of the time required for converging-beam scanning,and control of the superposition of beams, and focusing. Among them, thezone melting recrystallization method is maturest and has been used toproduce relatively-large-scale integrated circuits on an experimentalbasis, but it still causes a large amount of crystal defects such assub-grains to remain in the device, thereby failing to fabricateminor-carrier devices and to provide sufficiently excellent crystals.

[0016] The above method 2 that does not use the Si substrate as a seedfor epitaxial growth includes the following four methods.

[0017] (1) An oxide film is formed on an Si single crystal substratewith a V-shaped groove etched anisotropically in its surface, apolycrystal Si layer is deposited on the oxide film so as to be as thickas the Si substrate, and then an Si single crystal region surrounded bythe V-shaped groove so as to be separated dielectricly is formed on thethick polycrystal Si layer by polishing from the rear surface of the Sisubstrate. This method provides excellent crystallinity but the stepsfor depositing polycrystal Si by a thickness of several hundred micronsand polishing the single crystal Si substrate from its rear surface toleave only the separated Si active layer have problems in terms ofcontrollability and productivity.

[0018] (2) SIMOX (Separation by Ion-Implemented Oxygen) that forms anSiO₂ layer in an Si single crystal substrate by means of oxygen ionimplantation and that is the presently maturest technique due to itsexcellent compatibility with the Si process. To form an SiO₂ layer,however, 10¹⁸ ions/cm² or more of oxygen ions must be implanted,resulting in the need for a large amount of time for the implantation,thereby leading to reduced productivity. In addition, the costs ofwafers are high. Furthermore, this method cause a large amount ofcrystal defects to remain in the device and does not industriallyprovide a sufficient quality to fabricate minor-carrier devices.

[0019] (3) A method for forming an SOI structure by dielectricseparation through the oxidization of porous Si. In this method, anN-type Si layer is formed like an island on a surface of a P-type Sisingle crystal substrate by proton-ion implantation (Imai et al., J.Crystal Growth, vol. 63, 547 (1983)) or by epitaxial growth andpatterning. Only the P-type Si substrate is made porous by ananodization method using an HF solution in such a way that the porousregion surrounds the Si island from the surface, and the N-type Siisland is then oxidized at a high speed for dielectric separation. Inthis method, the separating Si region is determined prior to the devicestep, thereby limiting the degree of freedom of device design.

[0020] (4) A method for forming an SOI structure using thermal treatmentor an adhesive to bond an Si monocrystal substrate on a different Sisingle crystal substrate that is thermally oxidized is attractingattention. This method requires an active layer for a device to beformed as a uniformly thin film. That is, the thickness of aseveral-hundred-micron-thick Si single crystal substrate must be reducedto the order of micron or less.

[0021] The following two methods can be used to provide a thinner film.

[0022] 1) Thickness reduction by polishing

[0023] 2) Thickness reduction by selective etching

[0024] The polishing in 1) cannot provide uniformly thin films easily.In particular, if the thickness is reduced to the order of submicron,the thickness variation will be several tens %, resulting in a seriousproblem for providing uniformity. The difficulty in achieving uniformityfurther increases with increasing size of the substrate.

[0025] In addition, although the etching in 2) is supposed to beeffective in providing uniform thin films, it has the followingproblems.

[0026] The selection ratio is at most 102 and is insufficient.

[0027] The surface obtained after etching is bad.

[0028] The crystallinity of the SOI layer is bad due to the use of ionimplantation or epitaxial or heteroepitaxial growth on a highconcentration B-doped Si layer.

[0029] A semiconductor substrate formed by bonding requires twosubstrates, one of which is mostly uselessly removed and disposed ofthrough polishing and etching, thereby wasting limited global resources.Thus, SOI with bonding presently has many problems in terms of itscontrollability, uniformity, and costs.

[0030] In addition, generally due to the disorder of the crystalstructure of a light-transmissive substrate represented by glass, a thinfilm Si layer deposited on the substrate can only form an amorphouslayer or a polycrystal layer based on the disorder of substrates, andtherefore high-performance devices cannot be produced. This is becausesince amorphous structure of the substrate is amorphous, an excellentsingle crystal layer cannot be obtained by simply depositing an Silayer. The light-transmissive substrate is important in producing acontact sensor or a projection liquid-crystal image display device thatis a light-receiving element. Not only the improvement of pixels butalso a high-performance drive element are required to attain higherdensity, higher resolution, and finer definition of the pixels in thesensor or display device. Thus, to provide elements on thelight-transmissive substrate, a single crystal layer of an excellentcrystallinity is required.

[0031] Among such SOI substrate production methods, the method offorming a non-single-crystal semiconductor layer on a porous layer andtransferring the layer onto a supporting substrate via an insulatinglayer as disclosed in Japanese Patent Application Laid-Open No. 5-21338is very excellent due to the uniform thickness of the SOI layer, itscapability of maintaining the crystal-defect density of the SOI layer ata low level easily, the flatness of the surface of the SOI layer, noneed for an expensive apparatus of a special specification forfabrication, and the capability of using the same apparatus for variousSOI film thicknesses ranging from about several 100 Angstrom to 10micron.

[0032] Furthermore, by combining the above method with the methoddisclosed in Japanese Patent Application Laid-Open No. 7-302889, thatis, by forming a nonporous single crystal semiconductor layer on aporous layer formed on a first substrate, bonding the nonporous singlecrystal layer onto a second substrate via an insulating layer,separating the first substrate and the second substrate by the porouslayer without destruction, and smoothing the surface of the firstsubstrate and forming porous layer again for reuse, the first substratecan be used many times. This method can significantly reduce productioncosts and simplify the production steps.

[0033] There are several methods for separating the bonded substratesmutually to divide into the first substrate and the second substratewithout destruction. For example, one of them is to pull the substratein a direction vertical to the bonded surface. Another method is toapply a shearing stress in parallel with the bonded surface (forexample, moving the substrates in the opposite directions within planesin parallel with the bonded surface or rotating the substrates in thecircumferentially opposite directions). A pressure can be applied to thebonded surface in the vertical direction. Furthermore, a wave energysuch as ultrasonic waves can be applied to the separation region. Apeeling member (for example, a sharp blade such as a knife) can also beinserted into the separation region in parallel with the bonded surfacefrom the side of the bonded substrates. Furthermore, the expansionenergy of a material infiltrated into the porous layer that functions asthe separation region may be used. The porous layer functioning as theseparation region may also be thermally oxidized from the side of thebonded substrates to expand the volume of this layer. The porous layerfunctioning as the separation region may also be selectively etched fromthe side of the bonded substrates to separate the substrates. Finally, alayer formed by ion implantation to provide microcavities may be used asthe separation region and the substrates may then be irradiated withlaser beams from the normal direction of the bonded surface to heat theseparation region containing the microcavity for separation.

[0034] However, these methods for separating the two bonded substratesmutually are ideally excellent, but all of them are not suitable for theproduction of semiconductor substrates. One of the difficulties is thatthe bonded semiconductor substrates are generally shaped like discs andhave a small thickness, for example, 0.5 to 1.0 mm and that the bondedportion has few relatively large recesses on which a jig can be caught.Thus, a method of catching on an orientation flat portion of eachsubstrate a jig having a recessed portion that fits the orientation flatportion and rotating the substrates in parallel with the bonded surface,or a method of catching the jig on a small recessed portion made in thebonded portion in the side of the bonded substrates to peel them arelimited. The pressure-based separation requires a very large pressure,thereby forcing the size of the apparatus to be increased. In the waveenergy method, the wave irradiation method must be substantiallyimproved to irradiate the bonded substrates with wave energyefficiently, and immediately after separation, the separated substratesmay partly contact and damage each other. In the separation from theside, the substrates may be bent to allow only their sides to be peeled,with their central portions remaining unseparated. In the method ofinserting the peeling member into the separation region from the side ofthe bonded substrates, the insertion of the peeling member may damagethe bonded surface between the substrates due to the friction of thepeeling member and the substrates.

[0035] One solution for avoiding these problems is to reduce themechanical strength of the separation region appropriately. This method,however, may increase the possibility that the separation region isdestroyed by an external impact prior to the bonding of the substrates.In such a case, part of the destroyed separation region may becomeparticles and contaminate the inside of the production apparatus.Although the conventional separation methods have the major advantages,they still have the above problems.

SUMMARY OF THE INVENTION

[0036] It is an object of this invention to provide an improvedseparation method and apparatus that can separate the bonded substratesmutually without destruction to prevent the separated substrates frombeing damaged and that is unlikely to destroy the separation regionprior to the step of separating bonded substrates even when an externalforce is applied thereto, thereby preventing the production apparatusfrom being contaminated with particles.

[0037] The feature of this invention resides in that a composite memberhaving a plurality of members as mutually bonded is separated into aplurality of members at positions different from the bonded position(separation region) of the plurality of members by jetting a fluidagainst the composite member.

[0038] With respect to the separation method, the composite member maybe any member having a separation region inside, whereas with respect tothe semiconductor substrate production method, it must have thefollowing structure. A major example of the composite member is bondedsubstrates by bonding a first substrate and a second substrate, thefirst substrate being a semiconductor substrate in which a separationregion is formed as a layer in a portion located deeper than its surfaceand in parallel therewith and in which the surface and the portionshallower than it has no separation region. That is, when this inventionis applied to the semiconductor substrate production method, the membersobtained after separation are not the same as the first and secondsubstrates prior to bonding.

[0039] According to this invention, the separation region is located ata position different from the bonding interface (junction surface)between the first and second substrates. In the separation step, thesubstrates must be separated by the separation region located at theposition different from the bonding interface.

[0040] Thus, the separation region is adapted to be mechanically weakerthan the bonding interface so that the separation region is destroyedbefore the bonding interface. Thus, when the separation region isdestroyed, a portion of the surface side of the first substrate whichhas a predetermined thickness is separated from the first substratewhile remaining bonded on the second substrate, thereby transferring theportion to the second substrate. The separation region may be a porouslayer formed by the anodization method or a layer formed by ionimplantation to provide microcavities. These layers have a large amountof microcavities. This region may also be a heteroepitaxial layer inwhich distortion and defects are concentrated in crystal lattices.

[0041] The separation region may also be multiple layers of differentstructures. For example, it may consist of multiple porous layers havingdifferent porosities or a porous layer of a porosity changing in thedirection perpendicular to the layers, as required.

[0042] The layer transferred from the first substrate to the secondsubstrate by, for example, separating the composite member comprisingthe first and second substrates bonded together with each other via theinsulating layer is used as a semiconductor layer (an SOI layer) on theinsulating layer to fabricate a semiconductor device.

[0043] Jet of a fluid that can be used for the separation can beconducted by a so-called water jet method that injects a flow ofhigh-pressure water through a nozzle. Instead of water, this fluid maybe an organic solvent such as alcohol, an acid such as hydrofluoric ornitric acid, an alkali such as potassium hydroxide, or a liquid capableof selectively etching the separation region. A fluid consistingessentially of an abrasive particle-free liquid is preferable.Furthermore, a fluid consisting of a gas such as air, a nitrogen gas,carbon dioxide, or a rare gas may be used. A fluid consisting of a gasor plasma that can etch the separation region may also be used.

[0044] The above separation method can be applied to the semiconductorsubstrate production method to enable the following methods:

[0045] 1) A semiconductor substrate production method comprising thesteps of preparing a first substrate comprising a porous single crystalsemiconductor layer and a nonporous single crystal semiconductor layersequentially stacked on a substrate; bonding the first substrate and asecond substrate so as to provide a composite member having thenonporous single crystal semiconductor layer located inside; and jettinga fluid to the vicinity of the porous single crystal semiconductor layerin the composite member to separate the composite member at the poroussingle crystal semiconductor layer, or

[0046] 2) a semiconductor substrate production method comprising thesteps of implanting ions into a first substrate of a single crystalsemiconductor at a predetermined depth to form an ion-implanted layerthat can provide a microcavity layer; bonding the first substrate and asecond substrate via an insulating layer so as to provide a compositemember in which the ion-implanted surface of the first substrate islocated inside; and jetting a fluid against the vicinity of theion-implanted layer of the composite member to separate the compositemember at the ion-implanted layer. This invention thus provides thesemiconductor substrate production method that can solve theconventional problems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIGS. 1A, 1B and 1C are schematic views illustrating a method forseparating a composite member according to this invention;

[0048]FIGS. 2A and 2B are schematic views illustrating an example of amethod for separating the composite member using a fluid according tothis invention;

[0049]FIG. 3 is a perspective view showing an example of a separationapparatus according to this invention;

[0050]FIG. 4 is a sectional view showing another example of a separationapparatus according to this invention;

[0051]FIG. 5 is a perspective view showing yet another example of aseparation apparatus according to this invention;

[0052]FIG. 6 is a schematic view showing still another example of aseparation apparatus according to this invention;

[0053]FIG. 7 is a schematic view showing still another example of aseparation apparatus according to this invention;

[0054]FIG. 8 is a schematic view illustrating another example of amethod for separating a composite member using a fluid according to thisinvention;

[0055]FIG. 9 is a schematic view showing another example of a separationapparatus according to this invention;

[0056]FIGS. 10A and 10B are schematic views showing yet another exampleof a separation apparatus according to this invention;

[0057]FIG. 11 is a schematic view showing still another example of aseparation apparatus according to this invention;

[0058]FIG. 12 is a schematic view showing still another example of aseparation apparatus according to this invention;

[0059]FIG. 13 is a schematic view showing still another example of aseparation apparatus according to this invention;

[0060]FIG. 14 is a top view of another separation apparatus according tothis invention;

[0061]FIG. 15 is a side view of the separation apparatus shown in FIG.14;

[0062]FIG. 16 is a schematic view showing a state of separating thecomposite member;

[0063]FIG. 17 is a sectional view of the separation apparatus shown inFIG. 15, in its standby state;

[0064]FIG. 18 is a sectional view of the separation apparatus shown inFIG. 15, in its substrate-holding state;

[0065]FIG. 19 is a sectional view of the separation apparatus shown inFIG. 15, in its separating-operation starting state; and

[0066]FIG. 20 is a sectional view of the separation apparatus shown inFIG. 15, in its separating-operation ending state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067]FIGS. 1A to 1C are schematic views illustrating a method ofseparating a composite member according to this invention.

[0068]FIG. 1A shows a state prior to the bonding of a first member 1 anda second member 2. The first member 1 has inside a separation region 3which is a separation position of this member. The separation region 3shaped like a layer has a lower mechanical strength than a layer region5 located on the side of a bonding surface 4 a.

[0069] The two members 1 and 2 are bonded such that the bonding surface4 a is faced to a bonding surface 4 b in order to form a disc-likecomposite member having a bonding interface 14, as shown in FIG. 1B. Afluid 7 is jetted from a nozzle 8 toward the end of the separationregion 3 located on the side (end surface) 6 of the composite member.The separation region 3 against which the fluid 7 is jetted is removedor collapsed. Thus, the composite member is separated into two members11 and 12 at the separation region 3, as shown in FIG. 1C.

[0070] The layer region 5 is not present on a separation surface 13 a ofthe separated member 11, and a layer region 5 has been transferred ontoa bonding surface 4 b of the original second member 2 so as to expose aseparated surface 13 b.

[0071] Thus, a member having the thin layer region 5 on the secondmember 2 is obtained.

[0072] By forming the second member 2 and layer region 5 by usingdifferent materials, a member having a heterogeneous bonding can beproduced easily. Specific examples of such materials include conductors,semiconductors, and insulators, and two of which are selected to formthe second member 2 and the layer region 5.

[0073] In particular, silicon, quartz, glass, or silicon having aninsulating film formed on its surface is preferably used as the secondmember.

[0074] A semiconductor material such as silicon, silicon germanium,silicon carbide, gallium arsenide, or indium phosphorus is preferablyused as the layer region. The layer region of such a material maypartially include an thin insulating layer.

[0075] The most preferred composite member that is separated into atleast two is obtained by bonding two semiconductor substrates, or onesemiconductor substrate and one insulating substrate and is calledbonded substrates or bonded wafers.

[0076] Separating such a composite member provides a semiconductorsubstrate of an excellent SOI structure.

[0077] Prior to bonding, the separation region is desirably formedinside a substrate along the bonding surface.

[0078] The separation region may be fragile enough to allow thecomposite member to be separated into two at the separation region bythe jetted fluid and to prevent damage to other regions other than theseparation region.

[0079] Specifically, it can be made fragile by containing a plurality ofmicrocavities inside the separation region or implanting heterogeneousions to cause strain.

[0080] The microcavity is formed of pores of a porous body or bubblesgenerated by ion implantation, as described below. The separation regionis preferably 0.1 to 900 μm and more preferably 0.1 to 10 μm.

[0081] The flow of a fluid used to execute separation according to thisinvention can be implemented by jetting the fluid through a nozzle. Amethod for converting the injected flow into thin beams at a high speedand a high pressure may be the water jet method using water as the fluidsuch as that introduced in “Water Jet” Vol. 1, No. 1, p. 4. In the waterjet that can be used for this invention, high-pressure water atseveral-thousand kgf/cm² pressurized by a high-pressure pump is jettedthrough a thin nozzle and can cut or process ceramics, metal, concrete,resin, rubber, or wood (an abrasive material such as SiO₂ grains isadded to water if the material is hard), remove a paint film from asurface layer, or wash the surface of a member. The water jet has beenmainly used to remove a part of the material, as described above. Thatis, water jet cutting has been carried out to remove a cut edge from amain member, and the removal of the paint film and the washing of themember surface has been executed to remove unwanted portions. If thewater jet is used to form the flow of a fluid according to thisinvention, it can be jetted toward the bonding interface on the side(end surface) of bonded substrates to remove at least a part of theseparation region from the side. In this case, the water jet is jettedagainst the separation region exposed on the side of the bondedsubstrates and against a part of the first and second substrates in thevicinity of the separation region. Then, the separation region of a lowmechanical strength is removed or destroyed by the water jet to separatethe composite member into two substrates without damage to eachsubstrate. Even if the separation region is not exposed on the side butis instead covered with a certain thin layer for any reason, the waterjet may be used to remove the layer covering the separation region onthe side and then to remove the separation region exposed from the side.

[0082] Although not often used in the prior art, the water jet may bejetted against a small recessed portion on the side of two bondedchamfered substrates, that is, on their circumference to penetrate andextend microcavities or pores in the separation region of a fragilestructure to separate the bonded substrates. This operation is notintended to perform for cutting or removal, so little chips occur fromthe separation region and the composite member can be separated withoutthe need for abrasive particles or damage to surfaces obtained byseparation, even if the material of the separation region cannot beremoved by the water jet. This is not a cutting or polishing effect buta kind of wedge effect provided by the fluid. Thus, this is veryeffective if there is a recessed or narrow gap on the side of the bondedsubstrates and the jetting force of the water jet is applied in adirection in which the substrates are peeled off at the separationregion. To obtain a sufficient effect, the side of the bonded substratesis preferably recessed rather than protruding.

[0083]FIGS. 2A and 2B show this effect. In FIGS. 2A and 2B, 901 and 911indicate first substrates, 902 and 912 second substrates, 903 and 913separation regions, 904 and 914 semiconductor layers, 905 and 915insulating layers, 906 and 916 bonding interfaces, 907 a jet of a fluid,and 908 and 918 the directions of forces applied to the substrates bythe fluid.

[0084]FIG. 2A conceptually shows the direction of a force applied to thesubstrates by the water jet when the side of the end of the bondedsubstrates is recessed. The force is applied in a direction in which therecessed portion is extended, that is, in a direction in which thebonded substrates are peeled off. On the contrary, FIG. 2B conceptuallyshows the direction of a force applied to the substrates by the waterjet when the side of the end of the bonded substrates is protruding. Inthis case, a force is not applied in the direction in which the bondedsubstrates are peeled off, so the substrates cannot be separatedmutually unless a part of the separation region can be initiallyremoved.

[0085] Even if the separation region is not exposed on the side but isinstead covered with a certain thin layer for any reason, a sufficientseparation effect can be obtained when the side of the bonded substratesis recessed as described above because a force is applied in thedirection in which the vicinity of the separation region is extended todestroy the thin layer covering the separation region on the side andthen to extend and destroy the separation region. To efficiently receivethe flow of the water jet, the aperture width of the recessed portion isdesirably equal to or larger than the diameter of the water jet. Whenthis invention is applied to manufacture a semiconductor substrate,since the thickness of the first and second substrates is less than 1.0mm, the thickness of the bonded substrates, that is, of the compositemember is less than 2.0 mm. Since the aperture width of the recessedportion is normally about half this value, the diameter of the water jetis preferably 1.0 mm or less. Actually, a water jet of about 0.1 mmdiameter can be put to practical use.

[0086] The nozzle jetting the fluid may have any shape including acircle. A long slit-like nozzle can also be used. By jetting the fluidthrough such a nozzle, thin band-like flows can be formed.

[0087] Various jet conditions of the water jet can be selectedarbitrarily depending on the type of the separation region or the shapeof the side of the bonded substrates. For example, the pressure of thejet and its scanning speed, the diameter of the nozzle (≈the diameter ofthe water jet) and its shape, the distance between the nozzle and theseparation region, and the flow rate of the fluid are importantparameters.

[0088] In an actual separation step, separation can be achieved byscanning the nozzle along the bonded surface while jetting the water jetfrom a direction in parallel with the bonding surface or fixing thewater jet while moving the bonded substrates in parallel. In addition,the water jet may be scanned so as to draw a fan around the nozzle, orthe bonded substrates may be rotated around the position of the fixednozzle as a rotational center if, as is often the case, the bondedsubstrates are shaped like discs such as wafers with orientation flatsor notches. Furthermore, the water jet may be jetted against theseparation region from an angled direction as required instead ofplacing the nozzle in the same plane as the bonded interface. Thescanning of the water jet is not limited to these methods but may becarried out by any other method as required. Since the water jet has avery small diameter and the injection direction is almost parallel withthe surface of the substrate, vector resolution shows that a highpressure of several-thousand kgf/cm² is rarely applied to thesubstrates. Since the water jet applies a force of only several hundredgrams to the bonded substrates except for the separation region, thesubstrates are prevented from being destroyed.

[0089] Instead of water, an organic solvent such as alcohol, acid suchas hydrofluoric or nitric acid, or alkali such as potassium hydroxide,or a liquid that can selectively etch the separation region may be used.Furthermore, a gas such as air, nitrogen gas, carbon dioxide gas, orrare gas may be used as fluid. A gas or plasma that can etch theseparation region may also be used. As water to be used for a compositemember separation method introduced into the process of producing asemiconductor substrate, pure water with a minimized amount of animpurity metal and particles, and ultrapure water are desirably used,but the substrates may be washed and the impurity metal and particlesare removed after separation using the water jet, due to the perfectlow-temperature process. In particular, in this invention, the fluid ispreferably free of abrasive particles so as not to leave unwantedscratches in the substrates.

[0090] A semiconductor substrate according to this invention can be usedto fabricate a semiconductor device and to form a single crystalsemiconductor layer on the insulating layer into a fine structureinstead of an electronic device.

[0091]FIG. 3 is a schematic view showing a separation apparatusaccording to one embodiment of this invention.

[0092] Reference numeral 101 denotes bonded wafers as a compositemember; 102 a fluid jet nozzle; 103 a vertical movement mechanism foradjusting the vertical position of the nozzle 102; 104 a horizontalmovement mechanism for adjusting the horizontal position of the nozzle102; 115 a horizontal movement mechanism for adjusting the horizontalposition of the wafer; and 105 a wafer holder as a holder.

[0093] Reference numerals 113, 114, and 116 denote guides.

[0094] In the apparatus shown in FIG. 3, the wafer separation operationis performed by using the movement mechanisms 103, 104, and 115 to alignthe nozzle 102 with the end of the separation region of the wafer 101and jetting a highly pressurized fluid from the nozzle 102 to the end ofthe separation region on the side of the wafer 101 while moving thenozzle in the horizontal and vertical directions with the wafer 101remaining fixed.

[0095] Reference numeral 106 indicates a backing material used asrequired and consisting of a porous or nonporous elastic body.

[0096]FIG. 4 is a schematic perspective view showing another example ofa separation apparatus used for this invention. In FIG. 4, 401 indicatestwo semiconductor wafers of Si integrally bonded as a composite memberhaving inside a porous layer that acts as a separation region. Referencenumerals 403 and 404 indicate holders that suck and fix thesemiconductor wafer 401 using a vacuum chuck and that are rotatablymounted on the same rotating shaft. The holder 404 is fitted in abearing 408 and supported by a supporting stand 409, and its rear end isdirectly coupled to a rotating shaft of a speed control motor 410. Thus,controlling the motor 410 enables the holder 404 to be rotated at anyspeed. The other holder 403 is fitted in a bearing 411 and supported bythe supporting stand 409, and a compression spring 412 is providedbetween the rear end of the holder 403 and the supporting stand 409 toapply a force in a direction in which the holder 403 leaves thesemiconductor wafer 401.

[0097] The semiconductor wafer 401 is set so as to correspond to arecessed portion of a positioning pin 413 and is sucked and held by theholder 404. The holder 404 can hold the middle of the semiconductorwafer 401 by using the pin 413 to adjust the vertical position of thewafer 401. The holder 403 is moved leftward against the spring 412 to aposition at which it sucks and holds the semiconductor wafer 401. Inthis case, a rightward force is applied to the holder 403 by thecompression spring 412. The returning force applied by the compressionspring 412 and the force of the holder 403 for sucking the semiconductorwafer 401 are balanced so that the force of the compression spring 412will not cause the holder 403 to leave the wafer 401.

[0098] A fluid is fed from a jet pump 414 to the jet nozzle 402 andcontinues to be output until the jet fluid is stabilized. Once the flowof the fluid has been stabilized, the nozzle is moved, a shutter 406 isopened, and the fluid is jetted from the jet nozzle 402 to the side ofthe substrate 101 against the center of thickness of the semiconductorwafer 401. At this point, the holder 404 is rotated by the motor 410 torotate the semiconductor wafer 401 and holder 403. By jetting the fluidagainst the vicinity of the thickness-wise center of the semiconductorwafer 401, the semiconductor wafer 401 is extended to cause a porouslayer in the semiconductor wafer 401 that is relatively weak to bedestroyed and is finally separated into two.

[0099] As described above, the fluid is applied to the semiconductorwafer 401 uniformly and a rightward force is applied to the holder 403holding the semiconductor wafer 401, so that separated semiconductorwafers 401 are unlikely to slide after separation.

[0100] The bonded wafer 401 can also be separated by scanning the nozzle402 in parallel with the bonding interface (surface) of the bonded wafer401 without rotating the wafer 401. When, however, separation isexecuted by scanning the nozzle 402 without rotating the bonded wafer401, high-pressure water at 2000 kgf/cm² is required for a nozzlediameter of 0.15 mm, whereas only 200 kgf/cm² of pressure is requiredwhen separation is carried out by rotating the bonded wafer 401 with thenozzle 402 fixed.

[0101] This is because water is jetted to the center of the bonded wafer401 to enable the water pressure to act efficiently as an extendingforce compared with the scanning of the nozzle.

[0102] The following effects can be obtained by reducing the waterpressure.

[0103] 1) The wafer can be separated without destruction.

[0104] 2) A large number of jets can be simultaneously used due to theincreased available capacity of the pump.

[0105] 3) The size and weight of the pump can be reduced.

[0106] 4) A wider range of materials are available for the pump andpiping to allow the apparatus to easily utilize pure water.

[0107] 5) The sound of the pump and, in particular, of the jet isreduced to allow sound-proof measures to be taken easily.

[0108] The wafer holding means shown in FIG. 4 holds the wafer by usingthe holders 403 and 404 to pull the wafer from both sides, but the wafermay also be held by pressing it from both sides of the holders 403 and404. In this case, the high-pressure water also advances while extendingthe bonded wafer 401 to form a small gap in them, and finally separatesthem into two.

[0109] The smaller the contact portion between the holders 403 and 404and the bonded wafer 401 is, the more flexibly the bonded wafer 401 canmove when the high-pressure water extends the wafer 401. Stressconcentration caused by the excessively high pressure and the presenceof water in the separation interface of the bonded wafer 401 serve toprevent cracks and to allow the wafer to be extended easily. Thesepoints enable effective separation. For example, when the contactportion between the holders 403 and 404 and the bonded wafer 401 has adiameter of 30 mm or less, the bonded wafer 401 does not crack and canbe separated into two during a single rotation of the bonded wafer 401,under the conditions of the nozzle having a diameter of 0.2 mm and thepressure of 400 kgf/cm².

[0110] In addition, the larger the contact portion between the holders403 and 404 and the bonded wafer 401 is, the more firmly the rearsurface of the bonded wafer 401 is supported when the high-pressurewater extends the wafer 401, thereby preventing cracks duringseparation. When the contact portion between the holders 403 and 404 andthe bonded wafer 401 has a diameter of 100 mm or more, the bonded wafer401 can be separated into two without cracks under the conditions of thenozzle having a diameter of 0.2 mm and the pressure of 400 kgf/cm².

[0111] If foreign matters such as particles are sandwiched between theholder 403 or 404 and the bonded wafer 401, the bonded wafer 401 is nolonger held in the vertical direction to cause the nozzle 402 to beoffset from its perpendicular direction toward the top of the bondedwafer 401 to the longitudinal or lateral direction, thereby failing toeffectively hit the high-pressure fluid against the separation interfacein the wafer 401. To prevent this, the surfaces of the holders 403 and404 that contact the bonded wafer 401 can be formed with a large numberof fine protrusions to minimize the contact area in order to reduce theeffect of possible sandwiched foreign matters.

[0112] In the supporting apparatus shown in FIG. 4, the holder 404 isrotated to rotate the holder 403 with it, so that a slight force iseffected in the direction in which the rotation is stopped and torsionmay occur in the separation surface until the bonded wafer 401 isentirely separated. In this case, the holders 403 and 404 can be rotatedsynchronously to prevent torsion in the separation surface. This methodis described below in detail.

[0113]FIG. 5 shows another separation apparatus according to thisinvention. In this figure, numeral 204 indicates a waferhorizontal-drive mechanism, 205 a wafer carrier, and 206 a wafertransfer arm. As shown in this figure, the wafer cassette 205 is placedon a cassette stand 207 such that a wafer 201 is arranged in thehorizontal direction. The wafer 201 is loaded on a wafer supportingstand 204 using a wafer loading robot 206. The wafer supporting stand204 on which the wafer 201 is loaded is transferred to the position ofhigh-pressure jet nozzles 202 and 203 by a supporting stand movementmechanism such as a belt conveyor. A high-pressure fluid is jettedagainst a separation region in a recessed potion in the wafer formed bybevelling, through the nozzles 202 and 203 of a fluid jet apparatuslocated on the side of the wafer, from a direction parallel with thebonded interface (surface) in the bonded wafer. In this case, thenozzles are fixed and the bonded wafer is scanned in the horizontaldirection to receive the high-pressure fluid along the recessed portionformed by bevelling. One or both of the nozzles 202 and 203 may be usedas required.

[0114] This operation enables the wafer to be divided into two at aporous Si layer. Although not shown in the drawing, another loadingrobot stores the separated wafers as a first and a second substrates.

[0115] In the horizontal jet method, the wafer need not be fixed and,after separation, is unlikely to jump out from the wafer supportingstand 204 due to its own weight. Alternatively, after the wafer has beenloaded on the wafer supporting stand, a jump prevention pin may beinstalled on the top of the wafer so as to protrude from the wafersupporting stand 204 to over the wafer or the top of the wafer may bepressed softly.

[0116] Furthermore, a plurality of bonded wafers may be placed and setin the vertical direction relative to their surfaces, and one separationregion of the bonded wafers may then be separated through horizontalscanning. A wafer set jig may subsequently be moved in the verticaldirection over a distance equal to the wafer interval to allow thesecond separation region of the bonded wafer to be separatedsequentially through horizontal scanning similarly to the firstseparation of the bonded wafers.

[0117]FIG. 6 schematically shows another separation apparatus accordingto this invention. This figure conceptually shows a nozzle of a waterjet apparatus used in this embodiment and its movement. As shown in FIG.6, a bonded wafer 301 is held by a holder 310 so as to stand in thevertical direction. A high-pressure fluid is jetted against a recessedpotion of the wafer formed by bevelling, through the nozzle 302 of thejet apparatus located above the wafer, from a direction parallel withthe bonding interface (surface) of the bonded wafer. In this case, thenozzle 302 and a supporting point 303 that allows the nozzle tooscillate within a plane so as to draw a fan are placed in the sameplane as the bonded surface in the wafer. The nozzle is oscillatedwithin the bonded surface in the wafer to oscillate the flow of the jetwithin this surface. This operation enables the high-pressure jet to bemoved and jetted along the recessed portion or gap in the bondingportion in the edge of the bonded wafer. This in turn enables the fluidto be jetted against a wide separation region without the need for arobot that moves the nozzle within the bonding surface accurately or amore mechanically complicated mechanism for moving or rotating thebonded wafer.

[0118]FIG. 7 conceptually shows another separation apparatus accordingto this invention, that is, another method for jetting a jet 503 againstthe periphery of a bonded wafer 501. The bonded wafer 501 is fixed by aholder 510 and a nozzle 502 can be rotated around the wafer to allow thejet 503 to be jetted against the bonding portion all over the edge ofthe wafer. The center of the wafer is held and a rail (not shown in thedrawing) concentric with the wafer is installed around the wafer 501,and a jig 512 with the nozzle 502 fixed thereto can be slid on the railto allow the jet 503 to be jetted against the bonding portion fromaround the wafer 501.

[0119]FIG. 8 shows another example of a separation apparatus accordingto this invention. In this figure, 601 is a first wafer, 602 is a secondwafer, 603 is a bonding surface, 604 is a fluid jet, 605 is a directionof a force applied to the wafer by the fluid jet, and reference numeral606 indicates an angle between the fluid jet and the bonding surface.According to this embodiment, the positions of the nozzle 611 and holder610 are set so that the direction of the jet jetted from the nozzle 611is inclined at an angle a from a direction parallel with the separationsurface in the wafer.

[0120] The wafer can be held by the apparatus shown in FIG. 4 and thenozzle can be disposed as shown in FIG. 8 to jet the fluid against theside of the wafer. Since the jet 604 is inclined at an angle a (606)from the bonding surface 603, different pressures are applied to the twowafers 601 and 602. In the example shown in FIG. 8, a relatively smallforce is applied to the wafer 602 toward which the jet is inclined,whereas a larger force is applied to the opposite wafer 601. When thejet is inclined at a side opposite to the wafer in which porous Si isformed, porous Si or a microcavity layer can be destroyed easily. Thus,the bonded wafers are desirably installed such that the wafer 601contains porous Si.

[0121]FIG. 9 shows another separation apparatus according to thisinvention. In this figure, 705 and 706 are vertical drive mechanisms forfluid jet apparatus nozzles 702 and 703, 707 is a horizontal drivemechanism for a water jet apparatus nozzle 704, and 708 is a waferholder.

[0122] A shown in FIG. 9, the wafer holder 708 is used to hold bothsides of the bonded wafer 701 so as to stand in the vertical direction.In this case, a side of the wafer having an orientation flat portion isdirected upward. A high-pressure fluid is jetted against a recessedpotion or gap in the wafer 701 formed by bevelling, through the nozzles702, 703, and 704 of the plurality of (in this example, three) jetapparatuses located above or on the side of the wafer, from a directionparallel with the bonding interface (surface) in the bonded wafer. Theconfiguration of each nozzle is the same as in FIG. 3. In this case, theplurality of nozzles 702, 703, and 704 are scanned along guides 711,712, and 713 in a direction in which the high-pressure fluid moves alongthe gap formed by bevelling.

[0123] In this way, the bonded wafers are divided into two.

[0124] When only one nozzle is used, a high pressure is required that issufficient to separate the wafer over a distance corresponding to itsdiameter. When the pressure is only sufficient to separate the waferover a distance corresponding to its radius, the wafer must be turnedupside down and separated again over a distance corresponding to itsradius. The plurality of nozzles can be used to allow each nozzle toseparate the wafer only over a distance corresponding to its radius, andthe need to jet the high-pressure fluid against the wafer again afterturning it upside down is omitted, and the overall surface of the wafercan be separated during a single step.

[0125]FIGS. 10A and 10B show another separation apparatus according tothis invention. In this figure, 801 is bonded wafers as a compositemember, 802 is a nozzle for a fluid jet, and 803 is a fluid. Ahigh-pressure pure water is jetted against a gap in the wafer formed bybevelling, through the nozzle with slit-like openings of the jetapparatus located above or on the side of the wafer, from a directionparallel with the bonding interface (surface) in the bonded wafer whileallowing the bonded wafer to stand perpendicularly to the holder 811, asshown in FIGS. 10A and 10B. The slit is located parallel with thebonding interface (surface) in the bonded wafer and positioned so that alinear flow of water is jetted accurately against the gap in the waferformed by bevelling. A plurality of nozzles are scanned in a directionin which the high-pressure fluid moves along the gap formed bybevelling.

[0126] The need to scan the nozzle is omitted by increasing the lengthof the slit above the diameter of the wafer.

[0127] The effect of this slit-like nozzle is that the wafer can bedivided under a lower pressure than with a single nozzle of a very smalldiameter. Despite the low pressure, by increasing the area from whichthe high-pressure fluid is jetted, the energy used to separate the wafercan be increased to enable it to be divided easily.

[0128] Not only a nozzle having a slit-like opening but also a pluralityof nozzles 1202 placed closely in a line to jet a fluid against a bondedwafer 1201 as shown in FIG. 11 can be used for this invention to obtainsimilar results. Reference numeral 1211 indicates a wafer holder.

[0129]FIG. 12 shows another separation apparatus according to thisinvention which can use a plurality of jets to separate a plurality ofwafers at the same time. In a basic configuration of the apparatus inFIG. 12, components similar to those in FIG. 3 are installedindependently. A wafer 1001 a is set on a holder 1005 a. A high-pressurefluid jetted from a nozzle 1002 a hits against a bevelled portion of thewafer 1001 a. The nozzle 1002 a can be moved in a directionperpendicular to the sheet of the drawing by a horizontal-movementmechanism 1004 a while jetting the high-pressure fluid against thebevelled portion. A similar operation can be performed by the apparatusin the right of the figure having a nozzle 1002 b, a horizontal-movementmechanism 1004 b, and a holder 1005 b. This configuration doubles thethroughput. Although this figure shows two sets of the jet apparatus,three or more of such apparatuses may be installed.

[0130] In addition, when the high-pressure pump does not have a largecapacity, the right wafer can be changed while the left high-pressurefluid is being jetted, and vice versa. This requires only one set of aloader and an unloader robots.

[0131]FIG. 13 shows another separation apparatus according to thisinvention in which wafers 1101 a, 1101 b, 1101 c, 1101 d, and 1101 e areset on a wafer holding means 1105. A plurality of nozzles 1102 a to 1102e are installed in a set of nozzle movement mechanisms 1103 and 1104.The nozzle interval is the same as the wafer fixation interval. Theholding mechanism and nozzle movement method are similar to those inFIG. 3.

[0132] By using the central axis of each wafer for alignment, the fivewafers are each fixed between the holders 1115 a and 1115 b, between theholders 1115 b and 1115 c, between the holders 1115 c and 1115 d,between the holders 1115 d and 1115 e, or between the holders 1115 e and1115 f, all of which can move on a guide 1114 in the horizontaldirection.

[0133] A movable supply pipe 1112 acting as both a common fluid supplypipe and a nozzle vertical-movement mechanism is connected to the fivenozzles 1102 a to 1102 e via a distributor 1113.

[0134] After the amount and pressure of fluid jetted from each nozzlehave been stabilized at a nozzle standby position, all nozzles 1102 a to1102 e are moved along the guide 1111 to a wafer separation position andthen further advance along the guide 1111 to separate the wafers.

[0135] Once the separation has been finished, the amount of jetted fluidis reduced or the jetting is stopped to return the nozzles to theirstandby positions.

[0136] In the apparatuses shown in FIGS. 10A to 13, separation can becarried out by jetting the fluid while rotating the holders for thewafers to rotate the wafers.

[0137]FIGS. 14 and 15 are a top and a side views showing a separationapparatus for a composite member used for this invention.

[0138] This separation apparatus has a rotation synchronizationmechanism and can rotate a first holder for holding a first surface ofthe composite member and a second holder for holding a second surface ofthe composite member, at the same angular speed in the same direction.

[0139] When a rotational drive force is applied to only one surface ofthe composite member or synchronization such as that described above isnot provided, the following phenomenon is likely to occur.

[0140] Immediately before a wafer that is a composite member iscompletely separated over the entire wafer, there is a moment at which avery small region, which is finally separated, remains unseparatedsomewhere on the separation surface. The following two separation modescan be assumed depending on a position of this very small unseparatedregion.

[0141] A first mode is a case in which the unseparated region remainsalmost at the center of the separation surface and a second mode is acase in which it remains in an area other than the center. FIG. 16conceptually shows these modes.

[0142] The first mode occurs if separation progresses uniformly from thecircumference of the wafer toward its center or if the strength of thevicinity of the center of the separation surface is high. In this case,if a rotational drive force is applied to only one of the holders 21 ofone side of the wafer, this rotation causes the very small unseparatedregion to be twisted off and separated.

[0143] The second separation mode occurs if during the initial step offluid jetting, a crack extends over the radius of the wafer or longerfrom a certain circumferential portion resulting in quick separation orif the strength of areas other than the vicinity of the center of theseparation surface is high. In this case, if a rotational drive force isapplied to only one of the holders 21 of one side of the wafer, thisrotation causes sharing stress, thereby causing the very smallunseparated region to be separated.

[0144] This is because the opposite holder 22 is subjected to noindependent drive force and is only rotated through the wafer, causing aslight force to be effected in a direction in which the rotation of theholder 22 is stopped even if softly the holder 22 is held by a bearing.

[0145] Such torsion or shear causes complicated forces in directionsother than the vertical one to be applied to the separation surface,resulting in the unwanted separation of an area other than theseparation surface.

[0146] Thus, when the wafer is separated while being rotated and if thewafer is rotationally driven without allowing both sides of it tosynchronize mutually, separation may occur from a surface other than adesired separation surface or the wafer or an active layer may bedamaged. These phenomena may significantly reduce the yield.

[0147] A motor support 36 for supporting a motor 32 that can control thespeed and a pair of shaft supports 37 and 38 for rotatably supporting amotor shaft 31 are fixed on a supporting stand 40.

[0148] Furthermore, a first holder support 33 for rotatably supportingthe holder 21 and a second holder support 34 for rotatably supportingthe holder 22 are fixed on the supporting stand 40.

[0149] A timing pulley 29 mounted on the motor shaft 31 and a timingpulley 25 mounted at the rear end of a rotating shaft 23 of the holder21 are connected together in such a way as to rotate in the samedirection by means of a timing belt 27.

[0150] Likewise, a timing pulley 30 mounted on the motor shaft 31 and atiming pulley 26 mounted at the rear end of a rotating shaft 24 of theholder 22 are connected together in such a way as to rotate in the samedirection by means of a timing belt 28.

[0151] The pulleys 25 and 26 have the same driving radius, and thepulleys 29 and 30 have the same driving radius.

[0152] The timing belts 27 and 28 are the same.

[0153] A drive force from the motor 32 is transmitted from the shaft 31to the holders 21 and 22 via the pulleys and belts in order to rotatethe holders 21 and 22 at the same angular speed in the same directionwith the same timing.

[0154] In FIG. 15, 60 is a jet nozzle that jets a fluid and 61 is ashutter. For clarity, the illustration of the nozzle and shutter aresimplified.

[0155] The nozzle 60 is fixed on the supporting stand 40 using afixation jig (not shown), and a wafer positioning member 35 is providedon the supporting stand 40 so as to be aligned with the nozzle 60.

[0156]FIG. 17 is a partially sectional view of the holder of theseparation apparatus before it holds the wafer 20.

[0157] The holder 21 or 22 is an assembly of a holding section 45 a or46 a that actually sucks and holds a wafer; a fixation section 45 b or46 b that rotates the holding section 45 a or 46 a together with therotating shaft 23 or 24; and detents 41 and 42 or 43 and 44.

[0158] Using a tube 52 and a pressurized gas passed through apressurizing passage 56, the holding section 45 a can move against acompression spring (a coil spring 47) in a direction in which it leavesthe rotating shaft 23 (rightward in the figure).

[0159] An opening op is provided near the center of the holding section45 a and is in communication with a pressure reducing passage 55 in therotating shaft. Using a vacuum pump (not shown) connected to the openingop via a pressure reducing tube 51, vacuum is drawn into the opening opto reduce the atmospheric pressure.

[0160] The holder 21 or 22 is moved forward (rightward in the figure) byhaving its holder section 45 a that directly sucks the wafer, guided bythe rotating shaft 23, as shown in FIG. 17, and using the pressure ofair introduced from the pressurizing tube 52. The holder 21 or 22 ismoved backward (leftward in the figure) by the compression spring 47.The holding section 45 a rotates with the rotating shaft 23 using thedetents 41 and 42. Basically, the holder 22 is specularly symmetricalwith the holder 21 and has the same mechanism as it. To allow the bondedwafer 20 and nozzle 60 to be always set at specified positions when thebonded wafer 20 is positioned and held on the holder 22, pressure iscontrolled and adjusted so that a stronger force is applied to theholder 21 than to the holder 22 during a forward operation, while astronger force is applied to the holder 22 than to the holder 21 duringa backward operation.

[0161] The usage of this apparatus, that is, the method for separating acomposite member according to this invention is described below. Thebonded wafer 20 is set so as to fit on a notch in a positioning stand35, as shown in FIG. 17. Pressurized air is then introduced to cause theholding section 45 a to advance, thereby allowing the holder 21 to suckand hold the wafer, as shown in FIG. 18. The holder 21 can fit thebonded wafer 20 on the notch in the positioning stand 35 to hold thecenter of the bonded wafer 20. When the bonded wafer 20 is held in anaccurate position, the nozzle 60 is located perpendicularly to the topof the bonded wafer 20 and the distance between the bonded wafer 20 andthe nozzle 60 is 10 to 30 mm. The holding section 46 a of the holder 22is moved forward (leftward in the figure) to suck and hold the bondedwafer 20, and the feeding of pressurized air of the holding section 46 ais stopped. The bonded wafer 20 is stopped due to a force actingrightward in the figure which is an combination of a force effected bythe compression spring and a vacuum suction force. The force effected bythe compression spring does not exceed the force required by the holdingsection 46 a to suck the bonded wafer 20, so the vacuum destruction ofthe inside of the pressure reducing passage 55 or 57 does not occur,which may in turn eliminate the suction force to cause the wafer 20 tofall.

[0162] A fluid is then fed from a pump 62 to the nozzle 60 for aspecified period of time until the jetted fluid is stabilized. Once thefluid has been stabilized, the shutter 61 is opened to jet thehigh-pressure fluid from the nozzle 60 against the thickness-wise centerof the bonded wafer 20. At this point, the speed controller motor 32 isrotated to rotate the holders 21 and 22 in synchronism in order torotate the wafer 20. By jetting the high-pressure fluid against thethickness-wise center of the wafer 20, the high-pressure fluid alsoenters the separation region to extend the bonded wafer 20, therebyfinally separating it into two.

[0163] Since the high-pressure fluid is applied uniformly against thebonded wafer 20 and the holders 21 and 22 each apply a force in adirection in which the bonded wafer 20 is drawn, as described above,separated pieces further leave each other and are prevented fromsliding.

[0164] In addition, in the wafer supporting means shown in FIGS. 17 to20, the wafer is supported while being subjected to a force by theholders 21 and 22 in a direction in which the holders move backward fromthe wafer, but the holders 21 and 22 may effect a force in a forwarddirection and this pressure may be used to hold the wafer. In this case,the high-pressure fluid also advances while extending the bonded wafer20 to create a small gap, thereby finally causing the wafer to beseparated into two. In this method, if the holders 21 and 22 do notsynchronize mutually, the bonding surfaces of the separated piecesdamage each other due to sliding, whereas if the holders rotate insynchronism, no damage occurs. Furthermore, when a force is applied in adirection in which the holders 21 and 22 move backward, the wafer 20 ispulled to move backward during separation by the holders 21 and 22 andthere may occur a difference in the amount of displacement between aseparated portion and an unseparated portion to unbalance the bondedwafer 20, thereby causing a crack when the high-pressure fluid isjetted. If, however, a force is applied to the holders 21 and 22 in adirection in which they move forward, the bonded wafer 20 will maintainbalance to enable the wafer to be separated stably.

[0165] A high- or atmospheric-pressure fluid can be injected against theentirely separated wafer to effect a force in a direction in which itmoves backward in order to break the surface tension of interveningwater, thereby separating it into two completely.

[0166] As described above, the separation apparatus according to thisinvention sequentially or simultaneously separates one or more compositemembers using a fluid. The composite members may be juxtaposed in thenormal direction of the surface or in parallel with the surface.

[0167] Alternatively, the composite members may be rotated or movedparallel with the surface to receive the fluid, or the flow of the fluidmay be moved parallel with the surface so as to hit against the sides ofthe composite members, or the composite members and fluid may be movedtogether.

EXAMPLE 1

[0168] (One Porous Layer and Nozzle Scanning)

[0169] A first P-type (or N-type) single crystal Si substrate having aresistivity of 0.01 Ω·cm was placed in an HF solution for anodization.The anodization conditions are listed below.

[0170] Current density: 7 (mA·cm⁻²)

[0171] Anodization solution: HF: H₂ 0: C₂H₅OH=1:1:1

[0172] Time: 11 (minute)

[0173] Thickness of the porous Si layer: 12 (μm) The porous Si layer isalso used as a separation layer to form a high-quality epitaxial Silayer, that is, a single porous Si layer provides multiple functions.

[0174] The thickness of the porous Si layer is not limited to the abovevalue but may be between 0.1 and several hundred μm.

[0175] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0176] Source gas: SiH₂Cl₂/H₂

[0177] Gas flow rate: 0.5/180 l/min.

[0178] Gas pressure: 80 Torr

[0179] Temperature: 950° C.

[0180] Growth speed: 0.3 μm/min.

[0181] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0182] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for fiveminutes for bonding.

[0183] To separate the bonded substrate formed in this manner using theapparatus shown in FIG. 3, this bonded wafer was supported from bothsides by the wafer holders so as to stand perpendicularly. Anabrasive-material-free and high-pressure pure water was jetted at 2,000kgf/cm² from a 0.15-mm nozzle of a water jet apparatus located above thewafer against a gap in the wafer formed by bevelling, from a directionparallel with a bonding interface (surface) in the bonded wafer. Anozzle horizontal drive mechanism was used to scan the nozzle in adirection in which the high-pressure pure water moved along the gapformed by bevelling. In this case, when an elastomer 106 (e.g., Viton,fluoro rubber, or silicone rubber) was used in the portion in which thewafer and holder contact each other, the wafer could be opened in thevertical direction relative to its surface to allow the high-pressurewater to enter that part of the porous Si layer which was sandwiched bythe wafer holders, thereby enabling the wafer to be separated.

[0184] As a result, the SiO₂ layer, the epitaxial Si layer, and part ofthe porous Si layer which were originally formed on the surface of thefirst substrate were transferred to the second substrate. Only theremaining part of the porous Si layer remained on the surface of thefirst substrate.

[0185] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0186] The speed at which a nonporous Si single crystal is etched by theetching solution is very low, and the selective ratio of this etchingspeed and the etching speed of the porous layer is 1:10⁵ or more. Thus,the amount of the etched portion of the nonporous layer (about severaltens of Angstrom) corresponds to the practically negligible reduction ofthe thickness.

[0187] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0188] An observation of the cross section by a transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0189] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using aninteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0190] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0191] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 40%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused for the above process.

EXAMPLE 2

[0192] (Two Porous Layers and Nozzle Scanning)

[0193] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to two-step anodization in an HF solution toform two porous layers. The anodization conditions are listed below.

[0194] First Step:

[0195] Current density: 7 (mA cm⁻²)

[0196] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0197] Time: 5 (minute)

[0198] Thickness of the first porous Si layer: 4.5 (μm)

[0199] Second Step:

[0200] Current density: 30 (mA·cm²)

[0201] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0202] Time: 10 (second)

[0203] Thickness of the second porous Si layer: 0.2 (μm)

[0204] The two porous Si layers were formed, and the surface porous-Silayer anodized by a low current was used to form a high-qualityepitaxial Si layer while the lower porous Si layer anodized by a highcurrent was used as a separation layer. That is, the functions wereassigned to the different layers. Thus, the thickness of the low-currentporous Si layer is not limited to the above value but may be between 0.1to several hundred μm.

[0205] In addition, a third and subsequent layers may be formed on thesecond porous Si layer.

[0206] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3um on the porous Si layer. The growth conditions are listed below.

[0207] Source gas: SiH₂Cl₂/H₂

[0208] Gas flow rate: 0.5/180 l/min.

[0209] Gas pressure: 80 Torr

[0210] Temperature: 950° C.

[0211] Growth speed: 0.3 μm/min.

[0212] Furthermore, a 200 nm thick oxide film (an SiO2 layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0213] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for fiveminutes for bonding.

[0214] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 3. A separation process similar to that inEmbodiment 1 was used. As a result, the SiO₂ layer, the epitaxial Silayer, and part of the porous Si layer which were originally formed onthe surface of the first substrate were transferred to the secondsubstrate. Only the remaining part of the porous Si layer remained onthe surface of the first substrate.

[0215] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0216] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 200 nm±4 nm.

[0217] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0218] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0219] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0220] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

EXAMPLE 3

[0221] (Porous Si Layer+Separation Layer Formed by Ion Implantation andNozzle Scanning)

[0222] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0223] The anodization conditions are listed below.

[0224] Current density: 7 (mA cm⁻²)

[0225] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0226] Time: 11 (minute)

[0227] Thickness of the porous Si layer: 12 (μm)

[0228] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0229] Source gas: SiH₂Cl₂/H₂

[0230] Gas flow rate: 0.5/180 l/min.

[0231] Gas pressure: 80 Torr

[0232] Temperature: 950° C.

[0233] Growth speed: 0.3 μm/min.

[0234] Furthermore, a 200-nm oxide film (an Sio₂ layer) was formed onthe epitaxial Si layer as an insulating layer, using thermal oxidation.

[0235] Ions were implanted from the surface of the first substrate insuch a way that their projected flights exists within the epitaxiallayer/porous Si interface, the porous Si/substrate interface, or theporous Si layer. This allowed a layer acting as a separation layer to beformed at a depth corresponding to the projected flight as a strainlayer formed by microcavities or concentrated implanted ions.

[0236] After pre-treatment such as N₂ plasma processing, the surface ofa separately prepared second Si substrate was placed on the surface ofthe SiO₂ layer to contact them mutually. These substrates were thensubjected to thermal treatment at 600° C. for 10 hours for bonding.

[0237] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 3. A separation process similar to that inExample 1 was used. As a result, the SiO₂ layer, the epitaxial Si layer,and part of the porous Si layer which were originally formed on thesurface of the first substrate were transferred to the second substrate.Only the remaining part of the porous Si layer remained on the surfaceof the first substrate.

[0238] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0239] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0240] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0241] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0242] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0243] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0244] According to this example, the ion implantation was carried outafter the formation of the epitaxial Si layer, but ions may be implantedinto the porous Si layer or the porous Si/Si substrate interface priorto the epitaxial growth.

EXAMPLE 4

[0245] (Bubble Layer Formed by Ion Implantation and Nozzle Scanning)

[0246] A 200 nm thick oxide film (an SiO₂ layer) was formed on the firstsingle crystal Si layer as an insulating layer, using thermal oxidation.

[0247] Ions were implanted from the surface of the first substrate insuch a way that their projected flight exists within the Si substrate.This allowed a layer acting as a separation layer to be formed at adepth corresponding to the projected flight as a strain layer formed bymicrocavities or concentrated implanted ions.

[0248] After pre-treatment such as N₂ plasma processing, the surface ofa separately prepared second Si substrate was placed on the surface ofthe SiO₂ layer to contact them mutually. These substrates were thensubjected to thermal treatment at 600° C. for 10 hours for bonding.

[0249] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 3. A separation process similar to that inExample 1 was used.

[0250] As a result, the SiO₂ layer, the surface single crystal layer,and part of the separation layer which were originally formed on thesurface of the first substrate were transferred to the second substrate.Only the remaining part of the separation layer remained on the surfaceof the first substrate.

[0251] Subsequently, the separation layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the separation layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0252] This etching step may be omitted if the remaining separationlayer is sufficiently thin.

[0253] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the separation layer. When 100 points of theoverall surface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0254] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0255] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0256] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0257] In addition, the separation layer remaining on the firstsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0258] According to this example, the surface area of the Si wafer istransferred to the second substrate via the separation layer formed byion implantation, but an epi-wafer may be used to transfer the epitaxiallayer to the second substrate via the separation layer formed by ionimplantation. The following process is also possible. After the ionimplantation according to this example, the surface SiO₂ is removed andthe epitaxial layer and then the SiO₂ layer are formed, followed by thebonding step. The epitaxial layer is then transferred to the secondsubstrate via the separation layer formed by ion implantation. In thelatter case, the surface area of the Si wafer is also transferred.

EXAMPLE 5

[0259] (Horizontal Placement and Movement of the Wafer)

[0260] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0261] The anodization conditions are listed below.

[0262] Current density: 7 (mA·cm⁻²)

[0263] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0264] Time: 11 (minute)

[0265] Thickness of the porous Si layer: 12 (μm)

[0266] Porous Si was used to form a high-quality epitaxial Si layer andas a separation layer.

[0267] The thickness of the porous Si layer is not limited to the abovevalue but may be between 0.1 to several hundred μm.

[0268] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0269] Source gas: SiH₂Cl₂/H₂

[0270] Gas flow rate: 0.5/180 l/min

[0271] Gas pressure: 80 Torr

[0272] Temperature: 950° C.

[0273] Growth speed: 0.3 μm/min.

[0274] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0275] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for 5minutes for bonding.

[0276] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 5. The wafer cassette 205 was placed on thecassette base 207 in such a way that the wafer 201 extended in thehorizontal direction, as shown in FIG. 5. High-pressure pure water at2,000 kgf/cm² was jetted from the 0.15-mm nozzles 202 and 203 of thewater jet apparatus located on the side of the wafer against the bondingregion in the bonded wafer through the gap therein formed by bevelling,from a direction parallel with the bonding interface (surface) in thebonded wafer. The nozzles were fixed and the bonded wafer was scanned inthe horizontal direction to receive the high-pressure pure water alongthe gap formed by bevelling.

[0277] This operation allowed the wafer to be divided into two via theporous Si layer. Then, another loading robot was used to store andcollect the separated wafer as a first and a second substrates.

[0278] The SiO₂ layer, the epitaxial Si layer, and part of the porous Silayer which were originally formed on the surface of the first substratewere transferred to the second substrate. Only the remaining part of theporous Si layer remained on the surface of the first substrate.

[0279] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0280] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 200 nm±5 nm.

[0281] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0282] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0283] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0284] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

EXAMPLE 6

[0285] (Oscillation of the Nozzle)

[0286] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0287] The anodization conditions are listed below.

[0288] Current density: 7 (mA cm⁻²)

[0289] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0290] Time: 11 (minute)

[0291] Thickness of the porous Si layer: 12 (μm)

[0292] Porous Si was used to form a high-quality epitaxial Si layer andas a separation layer.

[0293] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0294] Source gas: SiH₂Cl₂/H₂

[0295] Gas flow rate: 0.5/180 l/min.

[0296] Gas pressure: 80 Torr

[0297] Temperature: 950° C.

[0298] Growth speed: 0.3 μm/min.

[0299] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0300] The surface of a separately prepared Si substrate was placed onthe surface of the SiO₂ layer to contact them mutually. These substrateswere then subjected to thermal treatment at 1180° C. for 5 minutes forbonding.

[0301] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 6. As shown in this figure, the bonded wafer301 was allowed to stand in the vertical direction, and high-pressurepure water at 2,000 kgf/cm² was jetted from the 0.15-mm nozzle 302 ofthe water jet apparatus located above the wafer against the bondingregion in the bonded wafer through the gap therein formed by bevelling,from a direction parallel with the bonding interface (surface) in thebonded wafer. Then, the nozzle 302 was oscillated within the same planeas the bonding surface in the wafer so as to draw a fan, in order tooscillate the flow of the jet within this plane.

[0302] This operation allowed the wafer to be divided into two via theporous Si layer. As a result, the SiO₂ layer, the epitaxial Si layer,and part of the porous Si layer which were originally formed on thesurface of the first substrate were transferred to the second substrate.Only the remaining part of the porous Si layer remained on the surfaceof the first substrate.

[0303] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0304] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0305] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0306] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0307] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0308] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0309] Similar results were obtained by separating wafers in which aseparation layer was formed according to Examples 2 to 4.

EXAMPLE 7

[0310] (Rotation of the Wafer)

[0311] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0312] The anodization conditions are listed below.

[0313] Current density: 7 (mA cm⁻²)

[0314] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0315] Time: 11 (minute)

[0316] Thickness of the porous Si layer: 12 (μm)

[0317] Porous Si was used to form a high-quality epitaxial Si layer andas a separation layer.

[0318] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0319] Source gas: SiH₂Cl₂/H₂

[0320] Gas flow rate: 0.5/180 l/min.

[0321] Gas pressure: 80 Torr

[0322] Temperature: 950° C.

[0323] Growth speed: 0.3 μm/min.

[0324] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0325] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for 5minutes for bonding.

[0326] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 4.

[0327] A bonded wafer 401 was allowed to stand in the verticaldirection.

[0328] The bonded wafer 401 was set so as to fit on a positioning pin413 and was sucked and held by a holder 404. After the bonded wafer 401was held in an accurate position so as to fit on the positioning pin413, the nozzle 402 was moved until it was located perpendicularly tothe top of the bonded wafer 401 and the distance between the wafer 401and the nozzle 402 was set at 15 mm. Then, a holder 403 was movedforward (leftward in the figure) via a bearing 411 until it sucked andheld the wafer 401.

[0329] Then, water without abrasive material grains was fed from a waterjet pump 414 to the nozzle 402 for a specified period of time until theinjected fluid was stabilized. Once the water had been stabilized, ashutter 406 was opened to inject the high-pressure pure water from thenozzle 402 against the thickness-wise center of the side of the bondedwafer 401. At this point, a holder 404 was rotated to rotate the bondedwafer 401 and holder 403. The high-pressure water also entered theporous Si layer to extend the bonded wafer 401, thereby enabling it tobe finally separated into two.

[0330] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0331] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 200 nm±3 nm.

[0332] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0333] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0334] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0335] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0336] Similar results were obtained by separating wafers in which aseparation layer was formed according to Examples 2 to 4.

EXAMPLE 8

[0337] (Diagonal Injection)

[0338] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0339] The anodization conditions are listed below.

[0340] Current density: 7 (mA·cm⁻²)

[0341] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0342] Time: 11 (minute)

[0343] Thickness of the porous Si layer: 12 (μm)

[0344] Porous Si was used to form a high-quality epitaxial Si layer andas a separation layer.

[0345] ,The thickness of the porous Si layer is not limited to the abovevalue but may be between 0.1 to several hundred μm.

[0346] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0347] Source gas: SiH₂C1 ₂/H₂

[0348] Gas flow rate: 0.5/180 l/min.

[0349] Gas pressure: 80 Torr

[0350] Temperature: 950° C.

[0351] Growth speed: 0.3 μm/min.

[0352] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0353] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for 5minutes for bonding.

[0354] A bonded wafer was allowed to stand in the vertical direction,and high-pressure pure water at 2,000 kgf/cm² was jetted from the0.15-mm diameter nozzle of the water jet apparatus located above thewafer against the bonding region in the bonded wafer through the gaptherein formed by bevelling, from a direction inclined at an angle afrom the bonding interface (surface).

[0355] The wafer was held by the apparatus shown in FIG. 4 and thenozzle was disposed as shown in FIG. 8 to inject the fluid against theside of the wafer.

[0356] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0357] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0358] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0359] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0360] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0361] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0362] Similar results were obtained by separating wafers in which aseparation layer was formed according to Examples 2 to 4.

EXAMPLE 9

[0363] (A Plurality of Jets)

[0364] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0365] The anodization conditions are listed below.

[0366] Current density: 7 (mA cm⁻²)

[0367] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0368] Time: 11 (minute)

[0369] Thickness of the porous Si layer: 12 (μm)

[0370] Porous Si was used to form a high-quality epitaxial Si layer andas a separation layer.

[0371] The thickness of the porous Si layer is not limited to the abovevalue but may be between 0.1 to several hundred μm.

[0372] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0373] Source gas: SiH₂Cl₂/H₂

[0374] Gas flow rate: 0.5/180 l/min.

[0375] Gas pressure: 80 Torr

[0376] Temperature: 950° C.

[0377] Growth speed: 0.3 μm/min.

[0378] Furthermore, a 200-nm oxide film (an SiO₂ layer) was formed onthe epitaxial Si layer, using thermal oxidation.

[0379] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for 5minutes for bonding.

[0380] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIG. 9.

[0381] A shown in FIG. 9, the wafer holder 708 was used to hold bothsides of the bonded wafer 701 so as to stand in the vertical direction.High-pressure pure water at 2,000 kgf/cm² was jetted against the gap inthe wafer 701 formed by bevelling, through the 0.15 mm nozzles 702 to704 of the three water jet apparatuses located above or on the side ofthe wafer, from a direction parallel with the bonding interface(surface) in the bonded wafer. A plurality of nozzles were scanned in adirection in which the high-pressure pure water moved along the gapformed by bevelling.

[0382] This operation allowed the wafer to be separated into two via theporous Si layer.

[0383] As a result, the SiO₂ layer, the epitaxial Si layer, and part ofthe porous Si layer which were originally formed on the surface of thefirst substrate were transferred to the second substrate. Only theremaining part of the porous Si layer remained on the surface of thefirst substrate.

[0384] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0385] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0386] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0387] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0388] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0389] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0390] Similar results were obtained by separating wafers in which aseparation layer was formed according to Examples 2 to 4.

[0391] The bonded wafer could also be separated efficiently by using aplurality of nozzles in the water jet injection methods according toExamples 5 to 8.

EXAMPLE 10

[0392] (Slit Jet)

[0393] A first P-type single crystal Si substrate having a resistivityof 0.01 Ω·cm was subjected to anodization in an HF solution.

[0394] The anodization conditions are listed below.

[0395] Current density: 7 (mA·cm⁻²)

[0396] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0397] Time: 11 (minute)

[0398] Thickness of the porous Si layer: 12 (μm)

[0399] Porous Si was used to form a high-quality epitaxial Si layer andas a separation layer.

[0400] The thickness of the porous Si layer is not limited to the abovevalue but may be between 0.1 to several hundred μm.

[0401] This substrate was oxidized in an oxygen atmosphere at 400° C.for one hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0402] Source gas: SiH₂Cl₂/H₂

[0403] Gas flow rate: 0.5/180 l/min.

[0404] Gas pressure: 80 Torr

[0405] Temperature: 950° C.

[0406] Growth speed: 0.3 μm/min.

[0407] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0408] The surface of a separately prepared second Si substrate wasplaced on the surface of the SiO₂ layer to contact them mutually. Thesesubstrates were then subjected to thermal treatment at 1180° C. for 5minutes for bonding.

[0409] The bonded substrate formed in this manner was separated usingthe apparatus shown in FIGS. 10A and 10B.

[0410] A shown in FIGS. 10A and 10B, the bonded wafer was allowed tostand in the vertical direction, and high-pressure pure water at 800kgf/cm² was jetted against the gap in the wafer formed by bevelling,through a slit-like nozzle of 0.15 mm width and 50 mm length of thewater jet apparatus located above or on the side of the wafer, from adirection parallel with the bonding interface (surface) in the bondedwafer. The slit was located parallel with the bonding interface(surface) in the bonded wafer and a linear flow of water was injectedaccurately against the gap in the wafer formed by bevelling. A pluralityof nozzles were scanned in a direction in which the high-pressure purewater moved along the gap formed by bevelling.

[0411] This operation allowed the wafer to be separated into two via theporous Si layer.

[0412] As a result, the SiO₂ layer, the epitaxial Si layer, and part ofthe porous Si layer which were originally formed on the surface of thefirst substrate were transferred to the second substrate. Only theremaining part of the porous Si layer remained on the surface of thefirst substrate.

[0413] Subsequently, the porous Si layer transferred to the secondsubstrate was selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. The single crystalSi layer remained without being etched, whereas the porous Si layer wasentirely removed by selective etching using the single crystal Si layeras an etch stop material.

[0414] The single crystal Si layer of 0.2 μm thickness was formed on theSi oxide film. The single crystal Si layer was not affected by theselective etching of the porous Si layer. When 100 points of the overallsurface of the single crystal Si layer formed were measured forthickness, the value obtained was 201 nm±4 nm.

[0415] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0416] Thermal treatment was further carried out in hydrogen at 1100° C.for one hour and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm and was similar to that of commerciallyavailable Si wafers.

[0417] Similar effects can be obtained by forming the oxide film on thesurface of the second substrate instead of the surface of the epitaxiallayer or forming it on both surfaces.

[0418] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,using hydrogen annealing or surface treatment such as surface polishing,the first or second substrate could be reused to repeat the aboveprocess.

[0419] Similar results were obtained by separating wafers in which aseparation layer was formed according to Examples 2 to 4.

EXAMPLE 11

[0420] (Quartz Substrate)

[0421] A light-transmissive substrate of quartz was prepared as a secondsubstrate.

[0422] N₂ plasma processing was applied to the surface of the quartzprior to bonding and thermal treatment was carried out at 400° C. for100 hours. Then, thermal treatment under hydrogen for flattening the SOIsurface after separation was carried out at less than 1000° C., in thiscase, 970° C. for 4 hours.

[0423] The other process is the same as in Examples 1 to 10.

[0424] If a transparent substrate of an insulating material is used asthe second substrate, the oxide film (the insulating layer) formed onthe surface of the epitaxial Si layer in Examples 1 to 10 is notnecessarily important. However, to space the epitaxial Si layer on whichelements such as transistors will subsequently be formed, from thebonding interface to reduce the effects of impurities in the interface,the oxide film (the insulating layer) is preferably formed.

EXAMPLE 12

[0425] (GaAs on Si) Examples 1 to 10 could be similarly implemented byforming the epitaxial layer of a compound semiconductor represented byGaAs.

[0426] In this case, the pressure of the water jet was maintained at 500to 3,500 kgf/cm² and the nozzle had a diameter of 0.1 mm or more (halfthat of the total bonded wafer thickness).

[0427] The method for allowing the GaAs epitaxial layer to grow on theporous Si layer is not limited to the CVD method but may be implementedby various methods such as the MBE, sputtering, and liquid phase growthmethods. The thickness of this layer is between several nm andseveral-hundred μm.

[0428] In each of these examples, the selective etching liquid for theion implantation layer or porous layer is not limited to the mixture of49% hydrofluoric acid and 30% hydrogen peroxide solution, but due to itsenormous surface area, the porous Si layer can be etched using thefollowing liquids:

[0429] Hydrofluoric acid;

[0430]

[0431] Hydrofluoric acid+alcohol;

[0432] Hydrofluoric acid+alcohol+hydrogen peroxide solution;

[0433] Buffered hydrofluoric acid;

[0434] Buffered hydrofluoric acid+alcohol;

[0435] Buffered hydrofluoric acid+hydrogen peroxide solution;

[0436] Buffered hydrofluoric acid+alcohol+hydrogen peroxide solution;

[0437] a mixture of hydrofluoric, nitric, and acetic acids.

[0438] The other steps are not limited to the conditions in theseexamples but various other conditions can be used.

EXAMPLE 13

[0439] (Rotation of the Wafer)

[0440] A disc-like P-type single crystal Si wafer having a resistivityof 0.01 Ω·cm was prepared as a first Si substrate and had its surfacesubjected to anodization in an HF solution.

[0441] The anodization conditions are listed below.

[0442] Current density: 7 (mA·cm⁻²)

[0443] Anodization solution: HF: H₂O: C₂H₅OH=1:1:1

[0444] Time: 11 (minute)

[0445] Thickness of the porous Si layer: 12 (μm)

[0446] This wafer was oxidized in an oxygen atmosphere at 400° C. forone hour. The oxidization caused the inner wall of the pores in theporous Si layer to be covered with a thermally oxidized film. Thesurface of the porous Si layer was treated with hydrofluoric acid toremove only the oxidized film on the surface of the porous Si layerwhile leaving the oxidized film on the inner wall of the pores, and theCVD was then used to allow single crystal Si to epitaxially grow by 0.3μm on the porous Si layer. The growth conditions are listed below.

[0447] Source gas: SiH₂Cl₂/H₂

[0448] Gas flow rate: 0.5/180 l/min.

[0449] Gas pressure: 80 Torr

[0450] Temperature: 950° C.

[0451] Growth speed: 0.3 μm/min.

[0452] Furthermore, a 200 nm thick oxide film (an SiO₂ layer) was formedon the epitaxial Si layer as an insulating layer, using thermaloxidation.

[0453] Besides the first substrate formed in this manner, a disc-like Siwafer was prepared as a second Si substrate.

[0454] The surface of the second Si substrate was placed on the surfaceof the SiO₂ layer of the first Si substrate to contact them mutually.These substrates were then subjected to thermal treatment at 1180° C.for 5 minutes for bonding.

[0455] Next, preparations were made to separate the composite memberconsisting of the bonded wafer using the apparatuses shown in FIGS. 14,15, and 17 to 20.

[0456] The wafer, which is the composite member, was located so as tostand in the vertical direction while fitting on the notch in thepositioning base 35.

[0457] Pressurized air was supplied from the tubes 52 and 54 to thepressurizing passage 56, and the holding sections 45 a and 46 a weremoved forward to the front and rear surfaces of the wafer, respectively,in order to abut the front and rear surfaces of the wafer with theholding surface of the holding sections 45 a and 46 a each having anopening op, respectively, as shown in FIG. 18.

[0458] Using the tubes 51 and 53, the wafer was sucked and fixed to theholding sections 45 a and 46 a. The supply of pressurized air wasstopped and tension was supplied to the wafer in the opposite normaldirections of the front and rear surfaces of the wafer using the springs47 and 48.

[0459] With the shutter 61 closed, pure water without abrasive grainswas fed forcefully from the pump 62 to the nozzle of 0.15 mm diameterand the pump 62 was operated to inject water at a pressure of about 200kgf/cm².

[0460] The positioning base 35 was moved to its standby position, andthe power to the motor 32 was turned on to transmit rotational driveforce via the shaft 31 and belts 27 and 28 in order to rotate theholders 21 and 22.

[0461] Since the wafer was sucked by the holding sections 45 a and 46 a,it started to rotate simultaneously with the holders 21 and 22 at thesame angular speed in the same direction.

[0462] The shutter 61 was opened to inject the water jet against theseparation portion in the side of the wafer, as shown in FIG. 19.

[0463] Water from the water jet apparatus entered the pores in theseparation portion to separate the wafer around the porous layer that isthe separation portion.

[0464] As the injection of the water jet and the rotation of the wafercontinue, the gap formed by separation gradually grew from the peripheryof the wafer toward its rotational center and the wafer could be finallyseparated as shown in FIG. 20.

[0465] Since the wafer was subjected to forces in the directions shownarrows TA and TB in FIG. 20, the wafer was separated as shown in FIG.20, simultaneously with the final separation of the rotational center ofthe wafer.

[0466] Subsequently, the forced feeding of water was stopped and theseparated wafer was removed from the holding sections 45 a and 46 a.

[0467] Subsequently, the remaining porous Si layer transferred to thesecond substrate was selectively etched by being stirred using a mixtureof 49% hydrofluoric acid and 30% hydrogen peroxide solution. Thetransferred single crystal Si layer under the porous layer remainedwithout being etched, whereas the porous Si layer was entirely removedby selective etching using the single crystal Si layer as an etch stopmaterial, thereby exposing the thin single crystal Si layer.

[0468] Thus, a first SOI substrate having the single crystal Si layer of0.2 μm thickness on the Si oxide film of the second substrate wasobtained. The single crystal Si layer was not affected by the selectiveetching of the porous Si layer. When 100 points of the overall surfaceof the single crystal Si layer formed were measured for thickness, thevalue obtained was 201 nm±2 nm.

[0469] An observation of the cross section by the transmission electronmicroscope indicated that new crystal defects did not occur in the Silayer and that excellent crystallinity was maintained.

[0470] Thermal treatment was further carried out in hydrogen at 1100° C.for 50 minutes and the surface roughness was evaluated using theinteratomic force microscope. The mean square roughness of a 50-μmsquare region was about 0.2 nm.

[0471] In addition, the porous Si layer remaining on the first substratewas selectively etched by being stirred using a mixture of 49%hydrofluoric acid and 30% hydrogen peroxide solution. Subsequently,surface treatment such as polishing was carried out.

[0472] The first substrate, which had been polished, was again subjectedto anodization to form a porous Si layer and nonporous single crystal Siwas allowed to grow thereon. The surface of the nonporous single crystalSi layer, which had grown epitaxially, was oxidized. Then, the surfaceof a separately prepared Si wafer that was a third substrate was bondedon the oxidized surface of the single crystal Si layer of the firstsubstrate.

[0473] The conditions for the above process were the same as those forthe first bonded-wafer production.

[0474] The wafer was again separated in the same manner as in the firstseparation method described above to obtain a second SOI substratehaving the single crystal Si layer on the insulating surface of thethird substrate.

[0475] The above process was repeated to recycle the first substrate inorder to fabricate a third and a fourth SOI substrates.

[0476] As described above, this invention enables a composite memberhaving a separation region inside to be separated into a plurality ofsmaller members around the separation region without damaging ordestructing those portions other than the separation region. Therefore,this invention enables semiconductor substrates with higher quality thanthe conventional ones to be fabricated easily and reliably with a highyield.

What is claimed is:
 1. A method of separating a composite member havinga plurality of members as mutually bonded, at a position different fromthe bonding position of the plurality of members, comprising jetting afluid against a side surface of the composite member to separate thecomposite member.
 2. The method according to claim 1 wherein thecomposite member has inside one of the members a separation regioncontaining microcavities and the fluid is jetted against theneighborhood of the separation region to separate it into the pluralityof members around the separation region.
 3. The method according toclaim 2 wherein a recessed portion is formed near the separation region,the recessed portion receiving the fluid to extend the separationregion.
 4. The method according to claim 2 wherein the separation regionhas a lower mechanical strength than the bonding position.
 5. The methodaccording to claim 2 wherein the separation region comprises a porouslayer formed by anodization.
 6. The method according to claim 2 whereinthe separation region can provide microcavities formed by ionimplantation.
 7. The method according to claim 1 wherein as the methodof jetting the fluid a water jet method that jets a flow ofhigh-pressure water from a nozzle is used.
 8. Members obtained by theseparation method according to claim
 1. 9. A method of producing asemiconductor substrate comprising the steps of: preparing on asubstrate a first substrate having a porous single crystal semiconductorlayer and a nonporous single crystal semiconductor layer provided on theporous single crystal semiconductor layer; bonding the first substrateto a second substrate to form a composite member; and jetting a fluid tothe vicinity of the porous single crystal semiconductor layer of thecomposite member to separate the composite member at the porous singlecrystal semiconductor layer.
 10. The method according to claim 9 whereina recessed portion is formed near the porous single crystalsemiconductor layer of the composite member, the recessed portionreceiving the fluid to extend the porous single crystal semiconductorlayer.
 11. The method according to claim 9 wherein the porous singlecrystal semiconductor layer has a lower mechanical strength than thebonding surface between the first and second substrates.
 12. The methodaccording to claim 9 wherein the porous single crystal semiconductorlayer is formed by anodization.
 13. The method according to claim 9wherein as the method of jetting the fluid a water jet method that jetsa flow of high-pressure water from a nozzle is used.
 14. The methodaccording to claim 9 wherein the first substrate is formed by partlymaking a single crystal silicon substrate porous to form a porous singlecrystal silicon layer and allowing a nonporous single crystal siliconlayer to grow epitaxially on the porous single crystal silicon layer.15. The method according to claim 14 wherein the first and secondsubstrates are bonded mutually via at least one insulating layer and theinsulating layer is formed by oxidizing the surface of the nonporoussingle crystal silicon layer.
 16. The method according to claim 9wherein the second substrate comprises a light-transmissive substrate.17. The method according to claim 9 wherein the second substratecomprises a silicon substrate.
 18. A method of producing a semiconductorsubstrate comprising the steps of: implanting ions into a firstsubstrate comprising a single crystal semiconductor at a predetermineddepth to form an ion-implanted layer such that a microcavity layer canbe obtained; bonding the first substrate and a second substrate to eachother via an insulating layer therebetween to form a composite member;and jetting a fluid against the vicinity of the ion-implanted layer ofthe composite member to separate the composite member a t theion-implanted layer.
 19. The method according to claim 18 wherein arecessed portion is formed near the ion-implanted layer in the compositemember, the recessed portion receiving the fluid to extend theion-implanted layer.
 20. The method according to claim 18 wherein theion-implanted layer has a lower mechanical strength than the bondingsurface between the first and second substrates.
 21. The methodaccording to claim 18 wherein as the method of jetting the fluid a waterjet method that jets a flow of high-pressure water from a nozzle isused.
 22. A semiconductor substrate produced by using the methodaccording to claim
 9. 23. A separation apparatus executing theseparation method according to claim
 1. 24. The separation apparatusaccording to claim 23 wherein a flow of the fluid is jetted by using thewater jet method for jetting a flow of high-pressure water from anozzle.
 25. The separation apparatus according to claim 24 wherein thecomposite member and the nozzle are moved relatively to scan the flow ofwater.
 26. The separation apparatus according to claim 25 wherein thecomposite member is fixed while the nozzle is scanned in order to scanthe flow of water.
 27. The separation apparatus according to claim 26having a holder for holding the composite member; a nozzle horizontalmovement mechanism for moving the nozzle in the horizontal directionalong the bonding position of the composite material; and a nozzlevertical movement mechanism for adjusting the vertical distance betweenthe composite member and the nozzle.
 28. The separation apparatusaccording to claim 26 having a mechanism for scanning the nozzle in sucha way as to draw a fan around a supporting point.
 29. The separationapparatus according to claim 26 wherein the nozzle rotates around thecomposite member.
 30. The separation apparatus according to claim 26including a plurality of the nozzles.
 31. The separation apparatusaccording to claim 25 wherein the composite member is scanned while thenozzle is fixed in order to scan the flow of water.
 32. The separationapparatus according to claim 31 having a rotation mechanism for rotatingthe composite member.
 33. The separation apparatus according to claim 32wherein the nozzle is located so as to be directed toward the rotationalcenter of the composite member.
 34. The separation apparatus accordingto claim 32 having a rotation holding member for holding the rotationalcenter of the composite member.
 35. A separation method comprising thesteps of: rotatably holding a first surface of a composite member havinga plurality of members as mutually bonded by using a first holder;rotatably holding a second surface of the disc-like composite member byusing a second holder; rotating the first and second holders insynchronism; jetting a fluid against the end surface of the compositemember, which is rotating; and separating the composite member into aplurality of members using as a starting point the portion on which thefluid has been jetted.
 36. The separation method according to claim 35wherein the fluid is jetted against a separation position different fromthe bonding position of the composite member.
 37. The separation methodaccording to claim 35 wherein a recessed portion is provided in the endsurface of the composite member and the fluid is jetted against thebottom of the recessed portion.
 38. A separation apparatus comprising afirst holder for rotatably holding a first surface of a disc-likecomposite member having a plurality of members as bonded mutually; asecond holder for rotatably holding a second surface of the disc-likecomposite member; synchronizing means for allowing the first and secondholders during rotation to synchronize mutually; and a nozzle that jetsa fluid against the end surface of the composite member, which isrotating, in order to separate the composite member into a plurality ofmembers using as a starting point the position on which the fluid hasbeen jetted.
 39. The separation apparatus according to claim 38 havingmeans for setting the position of the nozzle so that the fluid is jettedagainst a separation position different from the bonding position of thecomposite member.
 40. The separation apparatus according to claim 38wherein a recessed portion is provided in the end surface of thecomposite member and the apparatus has means for setting the position ofsaid nozzle so that the fluid is jetted against the bottom of therecessed portion.
 41. A method of separating a composite member having aplurality of members, at a region including cavities or pores,comprising jetting a fluid consisting essentially of an abrasiveparticle-free liquid against a side surface of the composite member toseparate the composite member.